The Common European Framework of Reference for Languages (CEFR, Council of Europe, 2001) currently functions as an instrument for educational policy and practice. The view of language proficiency on which it is based and the six proficiency levels it defines lack empirical support from language-use data. Several issues need to be investigated collaboratively by researchers working in the fields of first and second language acquisition, corpus linguistics and language assessment. These issues are concerned with (i) the CEFR’s failure to consistently distinguish between levels of language proficiency (static aspect) and language development (dynamic aspect), (ii) with the CEFR’s confounding of levels of language proficiency and intellectual abilities, and (iii) the potential problem of mismatches between second-language learners’ communicative and linguistic competences. Furthermore, from a more theoretical perspective, this paper proposes (iv) to investigate which CEFR proficiency levels are attainable by native speakers and (v) to empirically delineate the lexical, morpho-syntactic and pragmatic knowledge shared by all native speakers (called Basic Language Cognition).